Phase modulation detector circuits



April l1o, 194s.

M. G. CROSBY PHASE MODULATION DETECTOR CIRCUITS Filed June 10, 1942 2 Sheets-Sheet 1 INVENTOR Mae/MY Q Ceasar www ATTORNEY f Y I l l h f3 311 fm. 2f?? 1320@ 323 W 305i l w/m y g 310 A 50a/Ecs f* L i H l e. i512/ l INVIA-:NTOR v Ma/PAY (fase):

ATTORNEY PetentedApr. 10, 194.5

" i l 'l '2,373,546

vmuri-:1 3 ,STATES L PATENT. .oi-Pics asians l PHASE MonULA'rIoN nn'rncron cmcnrrs Murray` G. Crosby,

Riverhead, N. Y., assig'nor to Radio Corporation of America, a corporation of- Delaware f application June 1c, 1942, serial Nol 446,421

'1. claims. (c1. 2150-1-27) My present invention relates ,to phase modulation receivers, and more particularly to im-.

proved. and simplified forms of detectors of phase modulated (PM) carrier waves. y

I have -disclosed and claimed various types of phase modulation detector, circuits of the nltered carrier type in my U. S. Patent No. 2,081,588, granted May 25,1937; U. S. Patent No. 2,065,565, granted December 29, 1936, andU. S. Patent No.

2,063,588, granted December 8, 1936. Generally,

in which the detector network of tlie present in' vention functions, x Y v Fig. 3 illustrates a modified form yof the invention,

Fig. '4 illustrates a further modlcation of the' invention. v

in those circuits the phase modulated wave energy is subjected to a filtering step in order to remove the modulation side bands from the WaveV energy, the filtered carrier energy being combined with the unfiltered PM-wave energy to secure detection. However, these prior receiver circuits were somewhatcomplicated. In the various detection circuits described herein simplified and eiiicient arrangements are secured.

It may be stated that it is one o f the main objects of myl present invention to provide PM. detectors in ywhich three, or four, electrode crystal .filters maybe utilized to provide a filtered carrier; the filtered carrier being given a 90 degrees phase shift and recombined with the unfiltered PM energy in a detector so as to derive the modu-f lation signals which were originally appliedto the carrier at the PM transmitter.

Another object of my -invention is to utilize inl a PM detector circuit a crystal filter for providing carrier energy free of any modulation side bined filtered carrier venergy and unfiltered PM wave energy being performed by any one of various devices.

aforesaid ltype which are reliable in operation vand economical to manufacture and assemble.

The novel features which I believe to be characteristic of my invention are set forthwith parl ticularity in the vappended claims; the invention itself, however, as to .both its organization and method of opcrationwwill best be understoodby reference to the following description taken in dica'ted diagrammatically several circuit organizations whereby effect.

' In the drawings: Y Fig. 1 schematically"showsal PM receiver embodying the present invention,

Figs. 2a to 2d respectively show the manner my invention may be carried into Referring now to the` accompanying drawings,

wherein like reference characters in the different figures designate similar circuit'elements, the receiver of Pig. 1 is of the superheterodyne type. This typeof receiver is universally employed in the reception of PM wave energy or frequency `band components, and the rectification of commodulated (FM) carrier wave energy. The car- 'rier frequency of received PM wave energy may be located in lany band of ultra-high frequency, and it will be understood that the transmission channelwidth may be of any desired value. As ls'well known to those skilled in the art, at the transmitter the phase ofthe carrier energy is varied in accordance with vthe amplitude of the modulation signals. Unlike frequency modulation wherein the carrier frequency is deviated in accordance with the amplitude of the modulation signal frequencies, in PM transmission the rate of mean, or center, frequency deviation at the transmitter is greater at the higher modulation frequencies. The .receiver networks prior to the` ultra-high frequency carrier of the desired PM Wave Energy.

The amplified PM wave energy is supplied to a nrst detector network; locally produced oscilla-- tions are provided from aclocal oscillator. The localoscillations and the collected PM wave ener'gy are heterodyned in asuitable first detector,

v the resultant heterodyne energy being of intermediate "frequency (I. lit),A The I. F, energy is amplified in one or more stages of I. F. amplication. The numeral! designates the usual I. F. output transformer which feeds the demodulator network. `It will be understood that.

each of the primary and 'secondary circuits of transformer l is tuned to the predetermined opconnection with the drawings in which I have inerating I. F. value. A resistor is shown connected across the resonant primary circuit of transformer I so as to provide a pass band width sufiieientlyv broad to pass substantially all the components ofthe desired PM channel.

'I'he amplified PM energy developed across they t secondary circuit I' of transformei l is applied to the input electrodes 5 and 6 of piezo-electric crystal 2. The opposite end of the piezo-electric nant input circuit I'.

effect of a frequency control tube.

crystal 2 is located lbetween a lpair of spaced crystal voutput electrodes 4 `and 3. As shown in Fig. 1 the holders, or input electrodes, 5 and 6 are connected to the opposite sides of the'reso- I'he crystal output electrodes 4 and 3 are connectedv respectively to the anodes I2 and I3' of diode rectiiiers I2 and I3.

'Ihe cathodes of the diodes I2 and I3 are connected together by .series-connected resistors I4 and. I5. Each of these resistors is bypassed by a suitable condenser for I. F. currents, and the cathode of diode I3 is grounded. Anodes lI2' and I3 are' also connected by a second' pair of `series- 'arranged resistors 9` and III. The junction of resistors 9 and III is connected by an adjustable resistor II to the junction of resistors I4 and I5. The high potential side of input circuit I' is connected to the junction of resistors 9. and I through a path consisting of the condenser I'I andfadjustable resistor 8 arranged in series. The electrostatic shield I, shown by the dotted. line, is connected to the ground side of the input circuit I', the shield element 1 acting electrostatif cally to shield the injut electrodes .5-6 from the output electrodes 4 3. The modulation voltage is taken oif from the cathode endfof resistor I4, and the modulation voltage may be applied to the s Yinput terminals of a modulation voltage amplier.

Automaticv frequency control (AFC).voltage isv deri'ved from the cathode end of resistor I4. This AFC voltage is Vutilized to control the reactive Those skilled in the art are fully aware of themanner of providing the AFC action. It is suilcient for the purposes of this application to pointout that the frequency control tube has vits circuits connected` to the tank circuit of the oscillator so as to pro` vide a simulated reactance across the tank'circuit. The gain of the reactance tube is varied by the AFC bias applied over leadl I6, the AFC line including the filter network I6? which prevents pulsating voltage components from affecting the reactance tube. As is well understood? any shift in the mean frequency of the I. F. energy relativeto the predetermined I. F. value of the 4 input circuit I' results inproduction o f AFCbias changes of a polarity-and magnitude such as to A vary the frequency control tube'in-a sense to compensate for the aforesaid mean frequency shift. l, The crystal holderl shown in the. demodulator network is of a type more completely described in my aforesaid U. S. Patent No.` 2,065,565. The out- A put electrode `4 feeds filtered carrier energy directly to diode I2, while the output electrode 3 feeds iiltered carrier energy ofopposite phase 'directly to diode I3. There is fed through the VpathA comprising the blocking condenser I1. and

variable. resistor 8 unfiltered PM wavel energy. This unfiltered energyvis combined with the :Illtered carrier energy in resistor network "9--I Il-I I. Thus, it willbe seen that one diode receives a is on the opposite side of the' crystal from elec.-

l ,trode 4. It has been experimentally confirmed that this phase reversal exists.

menciona now. directed to Figs. 2a A2d 1x1- elusive, since the latter graphicallyaexplain -the Amanner in `which the input network of the def modulator functions. In Fig. 1 the .reference 2PM-converter" is applied above the demodulator input network to indicate that the-'function of energy. 'I'he operation of the demodulator de- Cil pends upon the combining of filtered PM carrier with uniltered PM wave energy with such a phase relation that'a carrier is provided which is combined with the `sidebands to form AM wave energy. The latter is'readily rect ed by the opposed diode rectiflers I2 and I3. i

Referring to Figs. 2a andf2b, they show 'the normal side band relations of an AM waveand A notedv from this iigure that the ltered PM car-l rier, which is rrepresented by C', is phase shifted 90 degrees with respect to the unfiltered carrier C. The combination of the ltered carrier C' and the side bands Siand S2 form an amplitude modulated wave as shown in Fig. 2a. The presence of the original carrier C tends to make the resulting combination wave a combination of phase and amplitude modulation. However, since there is an amplitude vmoizlulation component present, it

"degrees out4 of phase with vthat fed to the other diode. The presence of this 180. degrees relation between the envelopes of the two modulated waves may be observed by noting that the side bands are rotated towards the minimumresultant amplitude point in Fig. 2c, and towards the maximum resultant amplitude point in Fig. 2d.

able from the cathode end of'resistor I4, is fed through'the time constantirouit I6' to the control tube vso that the .carrier frequency is autof matically maintained in .tune withv the crystal filter frequency. The latter is, of course, the operating I. F. value. Carrier exaltation is :on'` trolled by variable resistor 8 which is made higher in value to increase thecarrier exaltation. The lower theA magnitude of resistor 8 the less will be the degree ofcanier exaltation. If desired. re- 't' sistor II could be made variable to effect control over the degreel of carrier exaltation. By "carrier Y exaltation is meant the relativeam'plication of the 'carrier with respectv tion components.

Referring now to the modification Vto the sideband inoduiashown in Fig. 3, there is shown a 'demodulator network wherein a multi-grid detector tube is utilized in conjunction with a three-electrode crystal holder to provide a highly simplified form .of PM detector. The I. F. energy is fed to the transf -former 20| whose primary and secondary circuits are each resonated to the I. F. value. Each of the primary `andsecondary circuits has a damping Yresistor shunted thereacross toprovide proper pass-bandwidth. .The thirdgrid Illof the detector tube m is connected to the his'h potential side yof secondary circuit 20| of transformer 20|.

The' piezo-electric crystal znz. which i tuned to the operating- I. F. valu e, three electrodes associated therewith. One of these electrodesv is f desisllted 202 and isconnected to the low potenmagnitude 'of the plate-to-cathodeimpedance oi' tupczizz f g 1 In one set vof operating' lconditions a type 6L?- at the plate cf the detector tube. This :cm

nected to the first grid 2| 'Ihe latter is connected back to groundthrough a grid return resister, while Vthe cathode of the detectortube is connected ,toground through the usual carrierbypassed biasing reslstorf209. The plate 2|2 ofV .the detector tube Bl is connected to a source of positive potenti/al. through the load resistor 201..

The screen grid electrodes of tube 200 are conthrough it, More detailed description 0f 'the mode of operation gf the multi-grid detector tube is disclosed in my aforesaid U. S. Patent No.-

lThe modification shown in Fig. '4 utilizes four-electrode shielded crystal iilter employed in nected to the-positive terminal of the direct .cur-

rent voltage `supply through a voltage reducing resistor 203. v i

c It will be seen, therefore, thatthe input and output`electrodes o'f the crystaLnlter are conn'ected to'respectlve grids 2I0 and 2| of the multi-grid vdetector tube.' The demodulated output energy appears across the plate resistor 201 which is bypassed for the intermediate frequency by meansof lcondenser 201.'. AFC bias may also betaken from the plate end of resistor 201. Duev to the fact that the plate of the detector tubehas a permanent positive p otential von it, the AFC biasobtaincd from the plate also has uns penna# nent positive potential. This may b e applied to a grid of the frequency control tube 2|2',if t lie amount corresponding to the permanent voltage from the detector plate.

positive potential source through resistor. 2l

The numeral 2|0' represents the bypassed In other words, the cathode of, control tube 2|2' is connected to the conjunction with a detector of the type which has been disclosed in my application Serial No.

-399,586, iiled June.25, 1941. In this form of demodulator circuit the transformer 30| has its secondary circuit arranged to be connected to 'the inputelectrodes 305 andl 3 00 of the piezoelectric crystal illter which` utilizes the crystal A'302. The output electrodes 304 and 303 are c'on: nected to the plates 3| and -3|2' of` respective rectiier tubes-3|| and 3|2. The electrostatic 'shield'301 is employed to shield theinput and Aoutput electrodes of the crystal filter.

'- The output load resistors 3|.3 and 3|4 are con-v nected in series betweenthe cathodes of the recti- 'l' iler'tubes.' The junction of ,the load resistors is cathode of4 theI latter is 'mad'e positive-by an cathode biasing resistor which is tappedatthe proper point to provide a connctionfor the lower c end. of resistor R1 .thereby to apply the proper bias to rst grid 2|3. Due tothe phase shifter network Ci-Ri connected to thelplate, there is appliedto grid 2 I 3 voltagewhich is in quadrature phasey relation with voltage developed across theoscillator tank circuit' (not' Shown) plate impedance 'of the control tube would be ef,-V

Iconnected to the junctionv of resistors 308 andA 30,9. .The latter resistors are arranged in'series between plates 3| and 3|2 '.f The control grids of the rectier'tubes are connected in commonto an adjustable tap 320. The latter isslidable along the .resistor 3|0; the lower end of the latter is connected to a line connecting the junctions of of resistor 3| 0 is connected through blocking condenser '3| 0' and lead SI5 to an adjustable contact 330. The latter may becorinected either to the high potential side of input circuit 30|' or to an Ali/I contact arranged to beconnected to the high potential side ofthe primary circuit of transf former 30|. Thus, when the tap 330 is connected It will be understood that the'plate of tube 2|2' 4is con-v" nected to the high alternating potential side off the tank. circuit. lIn other words, the cathode-tol;

' fectively connected across the oscillator tank cir-v` cuit. This impedancewillV simulate ajcapacitive reactance, since'the quadrature 'voltage for grid- 2| 3 is taken olf across the resistive component of the `phaseshifter, and leads the voltage applied to.

.to the AM contact the demodulator tube is used for detection, cf AM waves. when it is connected as shown in Fig. 4 the circuit is utilized to demodu- -late PM wave energy.

It will now be. seen that the iiltered PM wave energy is fed Idirectly to the plates of a pair of triode detectors 3H and `3|2. The unfiltered PM wave energy is f'ed through lead 3 5 and potentiomet'er 3|0- 320 to the grids of the detectors. The

I degreeV of carriervexaltation may be-adjusted by siiY the phase shiftergsincefthe phasev shifter current leads the voltage. The AFC bias is fed through the time constant network 2|! tothe third grid 2|5, and the variation of its bias determines the tube was used 'for tube 200; 800 ohmswas'the tion of the resistors 201 and 208; With these magnitude of resistor 203; andf+250 volts were-- .applied to the high Vvoltage terminalatthe 'june-H conditions a positive potential of 50 volts a pears permanent potential vmay be easily compensated l. for bymakingthejcathodeof the reactance Ytube 50 volts -more positive.; vThis increases the-cur- 'f rent through cathode'resistor 2|0'v s 'as to make nt of .-plie`d to bothfthe output is'proportional to the I product of the two voltages.

the cathode more positive than the end of resistor 201'to which theAFC lineis'connected. The operation of the detector of Fig. 3 .depends upon the'combination of the ltered and uniilv 'potentiometerslider 320. The detected modulation `signal voltage and AFC bias appears across f the differentially connected resistors `3|3and 3H.

T-he load resistors .are `bypassed for 1I. F. currents.

.The operation oithe circuit shown in Fig. 4

depends upon the same principle as that shown in Fig. 3. However, in Fig. 4` the iiltered and unltered'energies are fed to th/e plate andl grid of Vthe triode detectors, instead of to separate grids of'a multi-grid tube. 'I'he combination of energies takes place in the same manner, since Ain both types odetectors the-detected output is obtained by virtue of thefact that, the result is the product of the two signals applied to thetwo application points. That is,. the arrangement of theelectrodes in these tubes produces a condition such that .theoutputi's `directly -in proportion to the input in each one so that when voltages are ap- As stated beforelthe circuits shown in'Flgffima-y be converted for the reception of AM waves by 1 Y connecting lead 3|5 toe-the primary circuit of 'teied PM vwave energy in the vi'nultiegrid detector I tube.` This combination is effected with a 90 degrecs phase shift in the carrier; since the shielded' three-electrode crystal iilterinherently efects'la transformer 30| instead of to the secondary. makes use of the inherent'phase shift of 90| degrees in the transformer so that'the voltage fed 'nils to thetwo detector'g'ids have theproper zero,

degrees phase change as the carrier is passed manner. With 4 or 180 degrees, relationship for AM reception.

There is an inherent 90-degrees phase shift hetween the input and output electrodes of the crys tal filter, Hence, the two 90 degrees shifts are combined to form a zero, or 180 degrees, shift de- `pending-upon the polarity of the terminals of the transformer. The same mode of operation may be -applied to the; circuit of Fig. 3 in the same diisamplitudc moduiation phase adjustment, FC potentials must be obtained by anotherv device, since the phase is not proper to produce them on thesame detectors.

- in common to the high potential side oi said res;

on'ant circuit.' and an output load resistor connected between-the cathodes of the detector tubes.

4. In a modulated carrier wave detecting Syss tem, means for shifting the relative phase position 'of the carrier componentof the modulated wave comprising, a piezo-crystal carrier lter in a four-electrode holder, two of said electrodes serving as input terminals, the other two serving as push-pull output' terminals, and a coupling consisting of a condenser in series4 with an adjustable resistor .from one of said input termi- WhileI have indicated and described several',

systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular \'organizations shownand described, buil that many modiilc'atiops may be made without departing from the scope `of my invention, as set forth in the appended claims.

WhatIclaimis: l f

nals to the midpoint'of -said-push-pull output terminals. 4 1 A 5. In combination with a source of phase mcdulated wave energy. a pair of opposed rectiers having a common output circuit', means for trans 1 forming the phase`v modulated energy to ampli- `Al.' In combination with a source of -phasemodulated wave energy,'a pair of opposed rectiile'rs having a common output circuit, a resonant circuit tuned to the'meanfr'equency ofthephase modulated energy, a, piezo-electric crystallin-Iter' i' network having input4 electrodes connected. to

opposite sides 'ofcsaid resonant circuit and output electrodes connected to respective put electrodes of said rectiers, said lter fun tioning` to apply to said respective input electrodes substantially unmcdulated energy fof said mean frequency, and a condensive path free of any electron discharge device in shunt reiation with said crystal iilter .for applying uniiltered phase modulated energy from high alternating potential,

side of said resonant circuit to said rectiers.

2., 1n combination with a' source of phase modulatedwave energyfa converter network for converting the phase modulated energy to amplitude modulated energy, said network comprising a resonant circuit tuned to the mean frequency of the phase modulated energy, a piezo-'electric crystal lter network having input terminals connected to opposite sides ci' said resonant circuit,

are istor netwrk, said lter' netwo'rk having output rminals connected' to spaced points of eresistornetwork, apath consistngof a conden er and resistor inv series connected between the high potential side 'ofsaid resonant circuit and an intermediate .pointof said resistor-'network for modulated energy..

s. In combination with fa vresonant circuit to' which is applied phase modulated carrier Vwave energy, a pair of vpiezo-electric crystal iholders tude modulated energy comprising a circuit tuned tothe center' frequency -of the phase modulated energy. a crystal filter network connected between said tuned circuit and respective input electrodes of said rectiers, said illter functioning toapply to said respective input electrodes substantially unmodulated energy o f said center frequency, a path in shunt with said crystal filter forY applying unilltered phase modulated energy from said tuned circuit to said rectiilers, saidshunt path comprising a condenser iin series with an adjustable resistor.

6. yIn combination with a source oi phase modulated wavee'nergy, a network for-converting the phasemodulated' energy to amplitude modulated' energy, said network comprising a resonant circuit tuned to the mean frequency of the phase modulated energy, a crystal filter .having apair ofinput electrodes connected to opposite sides of said resbnanticircuit, 'said nl ter having apair (of output electrodes, a resistor network con- 40 nected between the output electrodes, a path com- `transmitting to the latter a portion of said phase A acting as input electrodes connected to'opposite sides of said resonant circuit, a second pair 'of crystalholders acting as output electrodes, a pair of triode detectors having their anodes` connected to respective ones of said output electrodes, means forl connecting the "control -grids of said ltriodes prising a condenser in series with a `resistor connected betweenA the 'high potential side of said of triode detectors having their anodes connected y to respectiveonesof said output electrodes, means lfor connecting the control `grids of said triodes in common to the Vhigh-potential side of said res-v onant circuit, an output load resistor connectedl between the cathodes of the detector tubes, and additionalmeans for selectively disconnecting the grids from the resonant circuit and connecting them to a wave energy lpoint prior to the resonant circuit.' s)

MURRAY G. CROSBY.

circuit 'tol 

